Concentric conductor transmission line



Oct. 8, 1940. 5 H v 2,216,893

CONCENTRIC CONDUCTOR TRANSMISSION LINE Filed March 24, 1938 FIG.

IIIIIIIIIII'II'I p IIII I" 111111111 I INVENTOR R H. SMITH ATTORNEY conductor at intervals therealong.

ratented Uct. 8, 1940 PATENT OFFICE coNoENmo connvc'roa TRANSMISSION Phillip H. Smith, Denvllle, N. J., assignor to mu Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application March 24, 1988, Serial No. 197,785

1 Claim. (Cl. 174-28) This invention relates to concentric conductor transmission lines, and more particularly to arrangements for retaining concentric spacing between the conductors of such lines.

One form of concentric conductor line known heretofore comprises a tubular inner conductor disposed in a tubular outer conductor and spaced concentrically therefrom by insulating rings or the like mounted on the periphery of the inner In such arrangement insulating rings are held in place on the inner conductor in one of the following ways: (a) friction, (b) crimping the inner conductor on both sides of the insulating ring, soldering metal rings on the inner conductor or both sides of the insulating ring and (d) springing resilient wires on the inner conductor on both sides of each insulator.

Accordingly, these insulating rings create gaps between themselves and the inner conductor along a radial extending from the center of the line, and in addition, introduced between the inner and outer conductors a relatively large mass of material which has a high dielectric constant compared to air or gas surrounding it and which. in addition to increasing the-dielectric losses that are proportional to the mass of this material, alters the distribution of the voltage gradient on the outer surface of the inner conductor. This distribution would be uniform for a line assumed to have a uniform air or gas dielectric interven ing exclusively between the inner and outer conductors, or a line provided with insulators having a dielectric constant equivalent to that of the surrounding air,or gas, if such were possible. However, since a solid material having a dielcc tric constant equivalent to that of air or gas is physically non-existent, the nearest approac the desired condition of a uniform air or ga electric is realized with an insulator having mitts mum mass.

These alterations in the distribution of voltage gradient cause substantial increases of voltage gradient in the vicinity of'the insulating rings and frequently result in the production of relazlvely steep voltage gradients on the outer sur- Face of the inner conductor, particularly if any gaps intervene between the inner conductor and ;he insulating rings. Consequently, there may be )roduced in the vicinity of the insulating rings :orona and flashover by signaling voltages ap- Jlied to the line and having magnitudes substan- ;ially less than those that would be transmitted iv a concentric line of the same cross-sectional iimensions and having air or gas dielectric interv concentric conductor line in which the inner consulator adapted to engage the inner s vening exclusively between the inner and outer conductors.

Also it may happen that either in slipping the outer conductor onto the inner conductor or in handling an assembled concentric conductor line 5 in the field the insulating rings would be subjected to longitudinal displacement on the inner conducton Such movement tends to change the concentric relation between the inner and outer conductors, thereby causing further variation in the distribution of the voltage gradient on the outer surface of the inner conductor.

Concentric conductor lines may be used in the transmission of high frequency signals in the manner disclosed in'the patent of L. Espenschied et al. No. 1,835,031, issued December 8, 1931.

It is an object of the invention to provide a concentric conductor system which, for a given cross-section and conductor diameter ratio, allows the efficient transmission of maximum sigac naling voltages, substantially equivalent to those that would be transmitted by a concentric conductor system of the same dimensions but em bodying ideal insulating arrangements. 7

It is another object of the invention to provide a concentric conductor transmission line having highly efficient insulation for the trans-' mission of signaling currents embracing a wide band of frequencies. i

it is still another object of the invention to provide a concentric transmission line that can be expeditiously assembled in both factory and field, and therefore one that is relatively inexpensive to manufacture.

It is a further object of the invention to provide a concentric conductor transmission line in which there is a minimum disturbance to the air or gas dielectric intervening between the inner and outer ccnductcn's.

It is a still further object of the invention to 40 provide a concentric conductor line in which concentric spacing is substantially maintained at all ts thereof,

in a preferred form the invention comprises a ductor is provided with a plurality of pairs of diametrically aligned openings spaced therealong in such manner that adjacent pairs are singularly disposed relative to each other. In each pair of 59 aligned openings is positioned an elon ed is the outer conductor. This arrangemen concentric spacing of the inner conductor wi the same amount of air dielectric at all points along the line.

The invention will be more readily understood from the following description taken together with the accompanying drawing in which:

Fig. 1 is a sectional view of a concentric conductor illustrating one form of insulator in accordance with the present invention;

Fig. 2 is an end view of Fig. 1;

Figs. 3, 4, 5, 6 and '7 are sectional views of a concentric conductor showing other forms of insulators contemplated in the present invention; and

Fig. 8 is an end view of Fig. '7.

In the following description the same reference numerals are used to indicate the same elements appearing in the several views.

Fig. 1 shows a concentric conductor comprising outer conductor I and inner conductor 6. The latter is provided with a plurality of pairs of diametrically aligned openings H and IS, the pairs being spaced at intervals therealong. Of each pair, opening I"! has a diameter that is preferably larger than that of opening l8. Preferably each opening I! is angularly disposed 120 degrees relative to adjacent openings l1 and each opening |8 is also similarly disposed relative to adjacent openings l8 shown in Fig. 2. An electrical insulator IQ of an elongated type having a rounded end and formed with a projection 2| on the opposite end is positioned in each pair of openings H and l8 such that the projection ii is inserted in the opening l8 and the rounded end 20 engages the inner surface of the outer conductor substantially in a. pointcontac't. Preferably, the diameters of the openings ll and I8 are such that the insulators l8 fit tightly therein so as to permit a minimum amount of air dielectric to intervene between the inner conductor and each insulator. To facilitate the assembling of the insulators IS on the inner conductor, each opening I"! is preferably formed with a rounded edge. This rounding has also been found desirable electrically. By eliminatin any sharp edge on the surface of the inner conductor at the insulator the voltage gradient is further reduced resulting in somewhat greater improvement of the flashover voltage. It is evident that adjacent pairs of aligned openings I! and I8 may be disposed on the inner conductor in any desired angular relation in addition to that mentioned above.

Fig. 3 illustrates an insulator assembly comprising diametrically cooperating members and 3|. The member 30 comprises a cylindrical portion 32 terminating in a rounded end 33 and a reduced cylindrical portion 34 terminating in a V-shaped end 35. The member 3| consists of a cylindrical portion 36 terminating in a.

rounded end 31 and a reduced cylindrical portion 38 terminating in a wedge-shaped end 39. The inner conductor is provided with a plurality of pairs of diametrically aligned openings 40, spaced at intervals therealong. Each insulator is assembled by so disposing reduced portions 34 and 38 in openings 40, 40 such that each wedge-shaped end 39 is seated in each V-shaped end 35. The shoulders 4|, 4| formed by the junction of the cylindrical portions 32 and 36 and the reduced portions 34 and 38, respectively, engage the outer surface of. the inner conductor and may be curvilinearly shaped as to be readily fitted to inner conductors of various diameters. The rounded ends 33 and 31 engages the inner surface of the outer conductor on diametrically opposite sections there of and substantially in a point-contact. Adjacent pairs of aligned openings 40, 40 may be angularly disposed and provided with diameters to accommodate the reduced portions 34 and 38 in the manner described above in connection with Fig. 1.

Fig. 4 delineates an insulator assembly comprising an elongated cylindrical member 44 having rounded opposite ends and positioned in diametrically aligned openings 45, 45, provided in the inner conductor as described above in connection with Fig. 3. Over each end of the member 44 is placed a. sleeve 46 of suitable insulating material and whose one end engages the inner surface of the outer conductor and the opposite end engages the outer surface of the inner conductor. Adjacent insulator assemblies are shown angularly disposed at 90 degrees although these may also be angularly disposed similarly as the insulators shown and described in connection with Fig. 1.

Fig. 5 shows an insulator assembly in which diametrically aligned openings 50, 50 are provided with threads to receive the threaded ends of diametrically aligned insulating members 5|, 5| each of which terminates on the opposite end in a rounded portion for engaging the inner surface of the outer conductor substantially in a point-contact. Adjacent aligned members 5|, 5| are angularly disposed at 90 degrees, although these may also be angularly disposed as the insulators shown and described in connection with Fig. 1.

Fig. 6 is similar to Fig. 4 except elongated insulator is held in place by a transverse insulating pin 6| extending through a midpoint aperture 64 therein and positioned in diametrically. aligned openings 62, 62 provided in the inner conductor at an angle of degrees relative to openings 45, 45. It is understood that the pins 6| as well as the insulators 60 are tightly fitted in the respective openings for the reason mentioned above in connection with similar elements in Fig. 1.

Figs. '7 and 8 are generally similar to Figs. 1 and 2. Fig. 7 illustrates an insulator 10 comprising a cylindrical portion H and a reduced cylindrical portion 12 which is disposed in diametrically aligned openings l3, 13 provided in the inner conductor. Shoulder 14 formed by the junction of the portions 1| and 12 and engaging the outer surface of the inner conductor is preferably shaped in a curvilinear manner so as to be readily fitted to inner conductors of various diameters. Fig. 8 shows adjacent insulators disposed angularly at degrees, although it is evident this disposition can be 90 degrees, or any desired angular relation.

In the above arrangements, it is obvious that the insulators are precluded from longitudinal displacement on the inner conductor either in the operation of (a) slipping the outer conductor onto the inner conductor and (b) in handling an assembled concentric conductor line in the field. Consequently, the concentric relation between the inner conductor and outer conductor is retained at all points along the line.

In addition, pin-type insulators with their minimum mass of high dielectric material intervening between the inner and outer conductors tend to cause minimum dielectric losses and also minimum disturbances in the distribution of the potential gradient on the outer surface of the inner conductor. This together with-the elimination of gaps between the insulators and inner conductor along a radial extending from the center of the line and the substantial reduction of air or gas dielectric between the inner conductor and the individual pin-type insulators, due to tight fit of insulators in associated openings in inner conductor, obviates the production of relatively steep voltage gradients on the outer surface of the I inner conductor in the vicinity of the insulators.

Consequently, signaling voltages that are substantially equivalent in magnitude to voltages allowed by a line of the same dimensions having air or gas dielectric intervening exclusively between the inner and outer conductors, or an air or flashover, and therefore may be transmitted thereover with increased efficiency.

Furthermore, it is evident that a pin-type insulating arrangement of the character described above lends itself to the facile assembly of a concentric conductor line or the expeditious replacement of defective insulators. In the latter event a defective insulator can be removed and replaced without disturbing the other insulators which is not so in the case of ring-type insulators as all insulators leading to the defective one must be removed before the latter can be replaced.

Also, it is understood that all openings in the inner conductor may be formed with rounded edges as shown relative to opening I! in Fig. 1 for the reason mentioned above in connection therewith.

While the invention is particularly described in connection with a concentric conductor line having a tubular inner conductor, it is obvious that it is equally well-suited to concentric conductor lines provided with solid inner conductors.

It is understood that the invention is capable of modifications other than those disclosed herein, and the scope thereof together with such modifications is defined in the appended claim.

What is claimed is:

In a concentric conductor transmission line comprising solid-walled tubular inner and outer conductors, said inner conductor having a plurality of pairs of diametrically aligned openings, each pair of openings being angularly disposed relative to adjacent pairs, and insulators for retaining concentric spacing between said conductors, each of said insulators engaging the inner surface of the outer conductor on diametrically opposite points and comprising an elongated member positioned in each pair of openings and a sleeve disposed on each of the opposite ends of said elongated member so as to extend be- PM H. mm.

tween said inner andouter conductors and to engage each thereof. 

